Principles of naval engineering - Historic Naval Ships Association

Chapter 14. -PIPING, FITTINGS, AND VALVESLOCK NUTADJUSTING SCREWADJUSTING SPRINGCONTROLLING DIAPHRAGMPISTON STEAM PORTAUXILIARY VALVEPISTONHIGH PRESSURE-PORTAUXILIARY VALVESPRINGLOW PRESSUREPORTMAIN VALVE SPRING--MAIN VALVEDRAIN CONNECTIONFigure 14-20.— Spring-loaded reducing valve.47.59Xby the reduced pressure steam. These two forcesare continually seeking to reach a state of balance;and, because of this, the discharge pressureof the steam is kept constant as long as theamount of steam used is kept within the capacityof the valve.There are two types of gas-loaded (or pneumaticpressure controlled) reducing valves. Onetype, shown in figure 14-21, is designed to regulatepressure in low temperature air, water, oil,or other fluids. The other type, shown in figure14-22, is designed to regulate pressure in hightemperature steam, hot water, or other fluids.Both types of valves operate on the principle thatthe pressure of an enclosed gas varies inverselyas its volume.We will consider first the valve for low temperatureservice (fig. 14-21). In this valve, arelatively small change in the large volume withinthe dome loading chamber produces only aslight pressure variation, while the slightestvariation in the small volume within the actuatingchamber creates an enormous change inpressure. The restricting orifice connectingthese two chambers governs the rate of pressureequalization by retarding the flow of gas from onechamber to another.The dome loading chamber is charged with airor some other compressible gas at a pressureequal to the desired reduced pressure. When thechamber is loaded, and the loading valve isclosed, the dome will retain its charge almostindefinitely. When the regulator is in operation,the trapped pressure within the dome passes intothe actuating chamber through the small separationplate orifice and moves the large flexible379